Method of longitudinally pre-polarizing bodies consisting of at least one layer of piezoelectric material



1963 J. M. BRUSSAARD ETA]. 3,071,3

- METHOD OF LONGITUDINALLY PRE-POLARIZING BODIES CONSISTING 0F AT LEAST ONE LAYER OF PIEZOELECTRIC MATERIAL Filed Feb. 15, 1958 INVENTORS JAN MMRTEN BRUSSAARD AN WILLEM HEKKERT BY M AG NT United States Patent 3,071,841 METHOD OF LONGITUDINALLY PIKE-POLARIZ- ING BODIES CONSISTING OF AT LEAST ONE LAYER OF PIEZOELECTRIC MATERIAL Jan Maarten Brussaard and Jan Willem Hekkert, Eindhoven, Netherlands, assignors to North American Philips Company Inc., New York, N.Y., a corporation of Delaware Filed Feb. 13, 1958, Ser. No. 715,044 Claims priority, application Netherlands Feb. 16, 1957 2 Claims. (Cl. 29-2535) The present invention relates to a method for the longitudinal pre-polarization of bodies consisting of at least one layer of homogeneous, polycrystalline, ceramic, piezoelectric material having remanent polarization properties, which pre-polarization occurs in a medium having a high breakdown-strength, the main faces of the layers being provided with a number of parallel electrodes located at right angles or substantially at right angles to the sense of polarization, while the polarization between adjacent pairs of electrodes is of opposite sense.

Longitudinal pre-polarization means that the remanent polarization extends substantially in the direction of the longitudinal axis of the body. For this purpose, the electrodes should theoretically be provided inside the material at right angles to the main surfaces of the body, but this is difficult to realize in practice. Since electrodes are usually provided on the main surfaces, the polarization also has a transverse component, but the distance measured in the longitudinal direction between the electrodes to which the polarization is applied wholly or in part may be chosen to be so large with respect to the thickness of the body that the influence of the transverse component of the remanent polarization is, in practice, negligible. The said distance in the longitudinal direction of the body measured between the electrodes of opposite polarity is preferably twice as large as the thickness of the body.

Such a method is known from USA. patent specification 2,540,187. It has a limitation in that, due to the placement of the several electrodes, the bundle of lines of force produced during pre-polarization passes in part along the surface of the body beyond the material, which often causes arcing-over along the surface.

The method according to the invention, in which this disadvantage occurs to a much lesserdegree, consists in that one polarity of the polarization voltage is applied to the electrodes resting on one main face, and the other polarity is applied to the electrodes resting on the other mainface between each two adjacent electrodes on the first-mentioned main face. In this manner, advantage is taken from the fact that, as a result of said placement of the electrodes the whole bundle of lines of force passes through the material.

A further advantage of the method according to the invention over that according to said U.S.A. patent specification is, that for obtaining the same capacity, half the electrode surface is sufiicient, while obtaining the same output voltage.

The invention is particularly advantageous when carry ing out this method in pre-polarizing large numbers of such bodies simultaneously. As a matter of fact, in the aforesaid known method, the bodies are pre-polarized in a bath containing oil as a medium having a high breakdown-strength, a breakdown then rendering the bath unsuitable for a next polarization, so that large-scale production is not feasible. When using the method according to theinvention this disadvantage occurs to a much lesser degree in large-scale pro-polarization, since, as mentioned above, the risk of arcing-over per se has already been reduced. In so far as arcing-over is still to be feared 3,071,841 Patented Jan. 8, 1963 under these greatly improved conditions as may occur in practice, this can be met in a preferred form of the method according to the invention when using as a medium having a high breakdown-strength a gaseous medium, preferably a fluorchloromethane, for example CF CI In order that the invention may be readily carried into effect, an example will now be described with reference to the accompanying drawing, in which FIG. 1 shows a member pre-polarized according to a known method, and

FIG. 2 shows a member pre-polarized with the aid of the method according to the invention.

In FIG. 1, the reference numeral 1 designates a body of ceramic, piezo-electric material, for example BaTiO the main faces of which are provided with electrodes 2, 3, 4, 5, 6 and 7. The electrodes 2, 3 and the electrodes 3, 4 on the upper main face each constitute a pair of electrodes, similarly the electrodes 5, 6 and 6, 7 respectively each constitute a pair of electrodes on the lower main face. In this known method, the pre-polarization is effected so as to be of opposite sense between adjacent pairs of electrodes (2, 3 and 3, 4). As a result of. the placement of the several pairs of electrodes the bundle of lines of forces passes in part along the surface beyond the material, as represented schematically in FIG. 1. This often gives rise to arcing-over along the surface of the body.

FIG. 2 shows a body of ceramic, piezo-electric material the main faces of which are provided with electrodes 9, 10 and 11. The method according to the invention consists in that one polarity of the polarization voltage is applied to electrodes 9, 10 resting on the upper main face, while the other polarity is applied to the electrode 11 on the lower main face between the two upper adjacent electrodes on the upper main face. In this manner, the electrodes 9, 11 on the one hand and the electrodes 10, 11 on the other hand constitute a pair of electrodes. As a result of this disposition of electrodes the whole bundle of lines of force passes through the material.

The electrodes 9, 10, 11 may be applied to the ceramic body by the nonal techniques, such as described in the U.S.A. Patent 2,540,187 with respect to the electrodes 2, 3, 4, 5, 6, 7.

What is claimed is:

1. A method of polarizing a ceramic, piezoelectric body comprising disposing on a first surface of the body a plurality of spaced, parallel electrodes; disposing on a second surface opposite the first surface of the body a plurality of spaced, parallel electrodes alternately disposed to be between the electrodes on the first surface of said body; interconnecting the electrodes on the first surface of said body and connecting said interconnected electrodes to one pole of a polarizing voltage source; interconnecting the electrodes on the second surface and connecting said interconnected electrodes to the other pole of said polarizing voltage source, thereby to establish mainly within the body and away from the surface a longitudinally alternating polarizing field; and applying said polarizing voltage to said electrodes while said body is disposed in a gaseous medium having a relatively high value of electrical breakdown intensity.

2. A method of polarizing a ceramic, piezoelectric body comprising disposing on a first surface of the body a plurality of spaced, parallel electrodes; disposing on a second surface opposite the first surface of the body a plurality of spaced, parallel electrodes alternately disposed to be between electrodes on the first surface of said body; interconnecting the electrodes on the first surface of said body and connecting said interconnected electrodes to one pole of a polarizing voltage source; interconnecting the electrodes on the second surface and connect- References Cited in the file of this patent ing said interconnected electrodes to the other pole of UNITED STATES PATENTS said olarizing volta e source, thereb to establish mainl withi n the body and a .way from the sur face a longitudinally 4O187 CherrY 1951 alternating polarizing field; and applying said polariz- 5 2,598,707 a l June 1952,

ing voltage to said electrodes while said body is in an Wllhams July 1953 atmosphere of fluorchloromethane. Mason et a1 'T 1954 2,706,326 Mason Apr. 19; 1955 2,724,171 Wallace Nov. 22, 1955 

1. A METHOD OF POLARIZING A CERAMIC, PIEZOELECTRIC BODY COMPRISING DISPOSING ON A FIRST SURFACE OF THE BODY A PLURALITY OF SPACED, PARALLEL ELECTRODES; DISPOSING ON A SECOND SURFACE OPPOSITE THE FIRST SURFACE OF THE BODY A PLURALITY OF SPACED, PARALLEL ELECTRODES ALTERNATELY DISPOSED TO BE BETWEEN THE ELECTRODES ON THE FIRST SURFACE OF SAID BODY; INTERCONNECTING THE ELECTRODES ON THE FIRST SURFACE OF SAID BODY AND CONNECTING SAID INTERCONNECTED ELECTRODES TO ONE POLE OF A POLARIZING VOLTAGE SOURCE; INTERCONNECTING THE ELECTRODES ON THE SECOND SURFACE AND CONNECTING SAID INTERCONNECTED ELECTRODES TO THE OTHER POLE OF SAID POLARIZING VOLTAGE SOURCE, THEREBY TO ESTABLISH MAINLY WITHIN THE BODY AND AWAY FROM THE SURFACE A LONGITUDINALLY ALTERNATING POLARIZING FIELD; AND APPLYING SAID POLARIZING VOLTAGE TO SAID ELECTRODES WHILE SAID BODY IS DISPOSED IN A GASEOUS MEDIUM HAVING A RELATIVELY HIGH VALUE OF ELECTRICAL BREAKDOWN INTENSITY. 